The present invention relates to the technical field of corneal transplants (i.e. penetrating keratoplastyxe2x80x94PK). More precisely, the present invention relates to a new, modified method of performing PK carried out employing new means and new operation conditions.
Although over the past decades PK surgery has undergone continuous refinement, said technique still needs several improvements.
Various instruments have been developed to improve the quality of trephination in both donor and recipient corneas, while countless suturing techniques have been employed to reduce tissue distortion and minimize postoperative refractive errors. Also donor grafts of different shape and profile have been envisaged in the past, which however did not find any practical application due to the lack of suitable means for their realization; see Corneal Graftsxe2x80x94Ed. B. W. Rycroftxe2x80x94Butterworth and Co. LTD Publisherxe2x80x94Londonxe2x80x94pp 90, 91, (1955).
Nevertheless, to date the basic concept of cutting a donor corneal disc with a xe2x80x9cperfectxe2x80x9d margin to fit a xe2x80x9cperfectxe2x80x9d hole in the recipient""s cornea has remained unvaried.
According to the known conventional PK method a full-thickness xe2x80x9cverticalxe2x80x9d i.e. xe2x80x9cedge to edgexe2x80x9d wound is made in the recipient cornea. This results in a quasi-cylindrical open bed, which is filled in by a donor graft complementary in shape. Regardless of how donor and recipient cornea fit, this type of wound requires relatively tight sutures to hold the edges together until healing is sufficient to withstand the effect of the intraocular pressure. Said healing requires, usually, not less than one year.
As a consequence of said tight sutures, refraction is not stable and astigmatism, often of the irregular type, cannot be adequately corrected in a relatively high number of patients as long as sutures are present. In addition, when sutures are removed, substantial changes in refraction are frequently seen, possibly resulting in anisometropia and/or high-degree astigmatism. Finally, wound dehiscence occurs after suture removal in up to 4% of cases, even if removal is performed more than one year after surgery.
In spite the excellent prognosis of PK, visual rehabilitation of patients undergoing this type of procedure is slow and frequently hampered by high-degree astigmatism, often of the irregular type (K. K. Assi, S. R. Zarnegar, D. J. Schanzlin, xe2x80x9cVisual Outcome after Penetrating Keratoplasty with Double Continuous or Combined Interrupted and Continuous Suture Wound Closurexe2x80x9d Am. J. Ophthalmol.; 114 pages 63-71 (1992)). Several factors, including host-graft disparity, trephination technique, and suturing technique, are felt to affect the regularity of graft curvature. In addition, even if all other variables could be theoretically optimized, recovery of vision can be delayed by corneal distortion secondary to the presence of sutures, as some degree of tension-induced xe2x80x9ctissue rollingxe2x80x9d is necessary in order to obtain a watertight wound. Healing of these xe2x80x9cverticalxe2x80x9d, edge-to-edge corneal wounds requires a minimum of 6 months and typically one year in adults. As a consequence, in a relatively high number of patients useful, stable vision is not achieved until many months after PK surgery, often not before suture removal (E. A. Davis et al. xe2x80x9cRefractive and Keratometric Results after Triple Procedure. Experience with Early and Late Removalxe2x80x9d Ophthalmology; 105, (1998) pages 624-630).
During recent years, different types of lamellar keratoplasty (LK) procedures have gained popularity among corneal surgeons in an attempt to transplant selected layers of the cornea, speeding wound healing while optimizing postoperative refraction. With these methods a xe2x80x9chorizontalxe2x80x9d, surface-to-surface surgical wound results and the intraocular pressure tend to make the layers adhere to each other rather than gape. Tight suturing is not necessary and removal can be safely performed much earlier than after conventional PK surgery. However, the presence of a lamellar tissue interface may reduce the quality of vision after LK compared to that obtained with PK surgery.
The scope of the present invention is that of solving the problems inherent in the above-described techniques. More specifically, scope of the invention is to provide a novel PK method causing reduced post-operative anisometropia and/or astigmatisms and having quicker wound-healing as compared to the conventional PK method and, yet, not being affected by the low quality of vision typical of LK.
The present invention is based on the surprising finding that in a PK method, the specifically selected shape of the donor insert, the strength and position of the suture and the treatment conditions may result in a new method which unexpectedly combines the advantageous properties of PK with those of LK techniques, namely the final optical superiority offered by the former with the short healing time and reduced post-operation defects typical of the latter. The present invention modifies the conventional PK technique, first of all, in that a full thickness donor graft having a novel specific profile, shaped as a xe2x80x9creverse mushroomxe2x80x9d (FIG. 1), is used to fill in the wound open in the recipient cornea and having complementary shape. Secondly, a lax suture is employed, which causes a reasonable, still acceptable, post-operation refractive astigmatism. Finally, the suture is removed as soon as a few months after surgery.
Hence, the object of the present invention is a method of performing a penetrating keratoplasty in living eye in which a full-thickness corneal graft obtained from a corneal donor is positioned in a full-thickness open bed in the recipient""s cornea, the graft is held with suture to prevent sliding out of position, and the suture is finally removed, said corneal graft being circular, having step-like edge-to-edge lateral profile with the diameter of the posterior surface being larger than the diameter of the anterior surface, said full-thickness open recipient bed being prepared to be essentially complementary to the donor corneal graft and said suture being so lax to induce a post-operation astigmatism not higher than 4 dioptres (D). The suture is normally removed not later than three months from surgery.
In particular, the donor graft consists of a central full-thickness part, surrounded by a posterior circular peripheral wing of deep stroma and endothelium preferably about 1.0 mm in width. The diameter of the internal, posterior surface of the donor graft is preferably about 9.0 mm, and the diameter of the external, anterior surface of the donor graft is preferably about 7.0 mm.
The donor graft is held in position with suture in a way that each suture bite exits the donor graft at the base of the circular peripheral wing, and passes through the superficial recipient""s lamellae at the end of the dissection so that the peripheral wing is left free to adhere to the posterior face of the dissected recipient""s cornea under the effect of intraocular pressure.
In a further object of the invention the suture is stabilized or replaced in part or completely by biological glue or by internal anchoring means.
The method of the present invention brings about many advantages over the conventional PK methods as shown by the results reported in the experimental part of the application.
First of all, the shape of the donor graft, in combination with the exact position of the bites of suture, leaves the donor peripheral wings free to adhere to the posterior surface of the dissected recipient cornea under the effect of the intraocular pressure. This means that, upon post-suture injection of balanced salt solution into the anterior chamber, the surgical wound is perfectly watertight already at this point, and, more importantly, regardless of the strength of the suture. Under these circumstances, a lax suture technique is employed, which is simply intended to prevent the sliding out of position of the graft. As a consequence, the laxity of the suture reduces drastically the refractive post-operation astigmatism, which is normally maintained less than 4 Dioptres, even before removal of the suture.
Another advantage of the method of the invention is that the healing process is dramatically speeded up. This allows having a full-thickness graft completely free of suture as early as about four or three or even less months after surgery, thus significantly shortening the time necessary for visual rehabilitation.
A still further advantage is that, due to the particular shape of the donor graft a greater number of endothelial cells can be transplanted while maintaining the anterior graft surface at a safe distance from the corneo-scleral limbus. Finally, no expensive instrumentation is required for the method of the invention, except for artificial anterior chamber, if whole globes are not available.
Donor graft: the portion of the donor""s cornea to be transplanted, otherwise said donor button.
Recipient bed: the corneal incision in the recipient""s living eye wherein the donor graft shall be placed.
Full-thickness: comprises all corneal layers.
Cardinal sutures: four sutures, each at one of the four cardinal points of the circular wound.
Circular running suture: a single suture along the complete circular wound.